This invention relates generally to medical devices and particularly to a device for removing blood clots, or thrombi, from body vessels, such as the small arteries associated with the brain.
The presence of blood clots or thrombus in the vascular system is a very dangerous condition that if left untreated can cause serious and potentially life-threatening disease. Thrombi within the vasculature can form as a result from a variety of causes, such as trauma, disease, surgery, stagnant flow of blood, and foreign devices in the vasculature. Typically, a thrombus present in an arterial blood vessel tends to migrate in the direction of flow from a large diameter artery to smaller diameter arteries. The thrombus continues to flow with the blood until it becomes lodged against the vessel wall and is unable to advance. In some instances, the thrombus partially or completely blocks blood flow through the artery thereby preventing blood from reaching the tissue disposed downstream of the thrombus. Denying blood flow for an extended period of time can result in damage or death of the tissue beyond this point. The result can be loss of toes or fingers, or even entire legs in more severe circumstances. Moreover, thrombi in the venous system can migrate to the lungs and become a pulmonary embolus, which is usually fatal. In other instances, thrombi can migrate into the cerebral circulation and cause stroke and death.
Currently, thrombus removal, or thrombectomy, may be performed in a variety of ways. For example, the clot may be dissolved through chemical lysis using drugs. While this method is adequate, clot lysis has significant disadvantages in that it is a very slow process taking hours or even days to complete. Additionally, the drugs utilized in clot lysis cause the blood to thin, thereby leaving a patient susceptible to serious hemorrhage complications.
Thrombectomy may also be performed using mechanical devices. Typically, these devices are inserted into a patient's vasculature and delivered to a treatment site over a guide wire using the Seldinger or modified Seldinger technique, which is well known in the art. Generally, these mechanical devices have the disadvantage that they are usually not strong enough or dense enough to adequately capture and remove a thrombus. This is because these devices must be small and flexible in order to negotiate the tortuous anatomy where clots are likely to be found.
One type of common thrombectomy device is a balloon that is inflated in a vessel and then withdrawn to pull a clot(s) into a conventional sheath. The sheath may then be withdrawn from the patient to remove the captured clot(s). Other devices are simple open ended catheters into which a clot is aspirated and removed from the patient.
Although adequate for some applications, these devices have disadvantages. For example, the balloon catheter devices must be first advanced through the clot before they can be inflated and retracted. The process of penetrating the clot with the balloon catheter device tends to push the clot deeper into the arterial circulation where it becomes even more difficult to remove. Further, this system is not well suited to small vessels (below about 3.5 mm) because the catheter portion begins to approach the size of the vessel being treated, making it even more difficult, if not impossible to penetrate the thrombus without pushing it further into the vessel. Additionally, these mechanical devices must be designed so that they do not damage the vessel wall during the thrombectomy process, which may result in further clotting. As a result, the structure of these devices is typically very flimsy, thus compromising the ability to actually retain the clot during the removal process.
These same issues also plague devices using wire spirals or coils that can be collapsed and expanded into the clot, or basket like devices that are expanded inside of or distal to the thrombus and then retracted in an effort to pull the thrombus out of the vessel. These devices frequently collapse during the withdrawal process or actually macerate the thrombus into finer clots which then can migrate farther downstream, making them even harder to capture.
Still other devices utilize corkscrew shaped members that are collapsed into an outer delivery sheath and passed through the clot before they can be deployed and retracted. The action of pushing a device through the center of the clot forces the clot deeper into the artery and may fragment the clot, making it an even more dangerous embolus. Typically, such corkscrew devices have a smooth rounded tip to prevent the corkscrew from penetrating the vessel wall or otherwise damaging the vessel wall as it is screwed into the clot. With these devices, however, the smooth, rounded central tip itself does not screw into the clot; rather the central tip is pushed into the clot and then the remainder of the corkscrew is screwed into the clot. As with basket, coil, and balloon devices, this pushing force may also force the thrombus deeper into the vessel. Further, the corkscrew also exerts a pulling force on the periphery of the clot in addition to the pushing force focused on the center of the clot. These counter forces tend to macerate or fragment the clot and result in only a small part of the clot being captured. Some corkscrew devices may substitute a sharp tip that can screw directly into the clot. However, sharp tips can penetrate the vessel wall just as easily as they can penetrate and capture the clot. Accordingly, such devices are seldom used since they carry the very high risk of penetrating the vessel wall. Further, when a bead or ball is applied to the tip of the device that is large enough to protect the vessel wall, it is usually so large that it will tend to push the clot distally rather than penetrate the clot such that the clot can be captured and removed.
Another disadvantage common to conventional balloon, coil, basket, and corkscrew thrombectomy devices is that they tend to have relatively large cross-sectional profiles and, in turn, are overly stiff for use in small tortuous vessels of the brain. Therefore, it has become apparent to the inventor that a need exists for an improved mechanical thrombectomy device.